. The long range goal of these studies is to identify, characterize and eventually interfere with the adherence mechanisms responsible for mucosal colonization of H. influenzae type b. This application seeks to study certain surface structures (pili) of H. influenzae b that mediate adherence to human epithelial cells, and to further define the role of pili in mucosal colonization. To achieve this goal, the applicant will examine chromosomal DNA from a variety of H. influenzae type b strains to determine their homology to the structural gene of a prototypic pili of the H. influenzae b (strain M43). This gene has been cloned and sequenced by the applicant. Pili deficient (p-) mutants are being constructed by insertion of the 2 kb omega fragment encoding spectinomycin and streptomycin resistance. This mutated gene will be inserted back into the M43p+ derivative, yielding isogeneic p-transformant. The strain will be tested for its ability to adhere to epithelia and colonize respiratory mucosa in a primate model. The applicant also seeks to sequence the regions surrounding the structural gene for evidence of other genes affecting pili expression. Transposon mutagenesis of these accessory genes will be used to evaluate their role and regulation of assembly or adherence. "Such mutants will be evaluated for functional pili by electron microscopy, by adherence assays, and hemagglutination". Information obtained from these studies will clearly define the role of pili in H. influenzae b mucosal colonization. From such knowledge gained within this application, strategies can be developed to interfere with epithelial cell adherence to prevent infection.